The disclosures herein relate generally to surgical instruments and more particularly to an instrument providing for a less invasive unicompartmental replacement procedure.
Unincompartmental knee replacement procedures ordinarily require a relatively large incision. The patella is usually displaced and inverted to obtain adequate exposure of the joint and the required anatomical references for proper alignment of cutting blocks and/or guides.
Routinely a rod, referred to as an intramedullary rod, is inserted into the femoral intramedullary canal from the distal end of the femur. This rod is used for alignment purposes for cutting block and/or guides.
This familiar method is considered an acceptable technique but is also know to cause trauma to the tissues involved. When a lesser amount of trauma is caused by a surgical procedure, less time is needed for patient recovery.
Most surgical techniques for a unicompartmental replacement procedure include a relatively large incision with displacement and/or inversion of the patella. This adequately exposes for femur for use of instrumentation to determine proper alignment and depth of bone resection.
A hole is typically drilled through the distal portion of the femur and into the intramedullary canal. This hole is relatively large and is required for the insertion of an intramedullary rod. The rod aligns itself with the inner canal of the femur, and then using other instruments which reference the intramedullary rod, the surgeon determines alignment of the joint.
One current system offers an extramedullary technique whereby the entire length of the canal is not violated. However, this technique is not entirely or truly extramedullary. A hole must still be drilled into the distal portion of the femur and a short portion of the canal is still violated. This drilling will normally require patella displacement.
Alignment is required for positioning of saw blocks and/or saw guides which are used during resection of the distal femur bone. This is a commonalty with all systems. During typical procedures, when the intramedullary rod is inserted into the intramedullary canal, a compressing of the natural materials and fluids inside the canal occurs. This can have undesirable consequences in some patients. Therefore, avoiding violation of the intramedullary canal during such a procedure is preferable.
Therefore, what is needed is an instrument and a method to lessen the morbidity of the exposure by precluding the need to displace and/or invert the patella, and to avoid violating the intramedullary canal while still allowing proper alignment of instrumentation for bone resection.
One embodiment, accordingly, provides a less invasive unicompartmental replacement surgical instrument and method for establishing and verifying cutting depth and alignment. To this end, the surgical instrument includes a distal saw drill guide, a rod adapter removably mounted on the distal saw drill guide and a modular alignment rod removably mounted on the rod adaptor.
Cutting depth may be verified by replacing the distal saw drill guide with a distal saw block and a stylus. Alignment may be verified by attaching the rod adaptor and the modular alignment rod to the distal saw block.
A principal advantage of this embodiment is that it provides for a less invasive unincompartmental replacement procedure which reduces the morbidity of exposure by avoiding the need to displace the patella, and also avoids violating the intramedullary canal.